ELECTRICAL
TRUCK SERVICE MANUAL
leaves a smaller area through which the current can
pass and reduces the efficiency of the system. If the
insulation of the starter cable is broken or worn away,
there is also danger of a violent short which might ruin
the battery or other parts or cause a damaging fire.
Hard Starting - Battery Not at Fault
Temperature plays an important part of battery
capacity, and the lower the temperature, the lower will be
its ability for doing work. With this in mind it will be seen
that a fully charged battery is only partially capable at
subzero temperatures. This fact, coupled with the
conditions in which many engines are found, brings
about complaints regarding the size, quality and
construction of the standard equipment battery.
Fig. 9 Proper Jumper Cable Connection
There are times when it is necessary to increase the
TESTING
size of the battery, but such action should not be
considered a "cure-all" for hard starting complaints
Specific Gravity Test or Hydrometer Reading
during winter months. Even when special equipment is
installed, it is still essential to:
Check the specific gravity of battery electrolyte to
determine the strength of the solution. Since acid is
1. Use lube oil with correct SAE rating for winter
heavier than water, the more acid in a solution the
service.
heavier it will be. If the battery is discharged, the acid
combines with the plates and leaves the solution lighter,
2. Maintain distributor points in good condition and
showing a lower hydrometer reading. Inversely, the acid
properly adjusted.
leaves the plates and reenters the solution as the battery
is charged, causing the solution to become heavier and
3. Have clean and properly gapped spark plug
resulting in a higher hydrometer reading.
electrodes.
The following chart (A) illustrates a typical range of
4. Have good compression in the engine.
specific gravity for a cell in various stages of charge with
respect to its ability to crank the engine at 80F.
5. Maintain all joints and connections between
carburetor, manifolds and engine in a gas tight
Hydrometer Reading
Useful Capacity
condition.
1.260 Sp. Gr.
100%to Charge
1.230 Sp. Gr.
75%o Charge
6. Ascertain that automatic choke and choke plate are
1.200 Sp. Gr.
50% Charge
operating properly.
1.170 Sp. Gr.
25% Charge
1.140 Sp. Gr.
Very Little
7. Determine that engine and cab are well grounded
1.110 Sp. Gr.
None
and that ground straps are securely fastened to
clean contacts.
CHART A
Using Jumper Cables and Booster Battery for Starting
In reading a hydrometer, Fig. 10, barrel must be
When starting vehicles with a booster battery and
held vertically with just the right amount of acid drawn
jumper cables always use a booster battery having the
into the barrel, with bulb fully expanded, to lift the float.
same voltage as that in the vehicle to be started. To use
Float must not touch side, top or bottom stoppers of
a twelve-volt battery to start a vehicle equipped with a
barrel.
6volt system will impose a heavy electrical load on the
6volt starting motor, which may result in starting motor
damage. Fig. 9 illustrates correct method for connecting
jumper cables from one battery to another.
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